The present invention relates to the cross-linking of polymers by means of a cross-linking agent. For this purpose use is generally made of organic peroxides. The peroxides that are mostly used in actual practice are dicumyl peroxide, di-t-butyl peroxide, bis(t-butylperoxyisopropyl)benzene and 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane. A number of hydroxylamines are known from German Patent Application 27 05 034 (a counterpart to U.S. Pat. No. 4,207,091), Archive der Pharmazie 292, 329 (1959) and Liebigs Annalen Chem. 606, 24 (1957) and from the latter publication it is also known that upon being heated, some hydroxyl amines will decompose into radical fragments with which acrylonitrile may be polymerized. The present process, however, relates to the cross-linking of polymers and consequently to a different type of reaction.